Alpha dose

Harley, N., and B. C. Pasternack, Environmental Radon Daughter Alpha Dose Factors in a Five-Lobed Human Lung, Health Phvs. 42 789 (1982). 

The lung cancer risk from radon daughter exposure is known only for occupationally exposed males. In order to determine the risk in environmental situations it is necessary to determine whether the bronchial alpha dose, which confers the risk, is similar to that in mines. 

Particle size is a major factor which determines the alpha dose conversion factor for radon daughters (mGy/WLM). Data on indoor environments are emerging and indicate that a variety of specific conditions exist. For example, a dose factor four times that for a nominal occupational or environmental exposure exists if kerosene heater particles dominate the indoor aerosol and four times smaller if a hygroscopic particle dominates. 

In the present study the bronchial morphometry of Yeh and Schum (1980) is utilized instead of the Weibel model. This is a more accurate description of the bronchial airway lengths, diameters and branching pattern. It does not assume dichotomous branching and therefore does not suffer from the problem of the artificially high surface area leading to low alpha dose in the more distal airways common to other models of the human airways. 

The calculations are shown for the adult male breathing under normal environmental conditions. The alpha dose combines the daytime and nighttime breathing patterns. 

Table II shows the nominal alpha dose factors for occupational mining exposure. Table III shows the alpha dose factors for the nominal environmental situation. Table IV shows the bronchial dose factors for the smallest sized particles, that dominated by the kerosene heater or 0.03 pm. particles. The radon daughter equilibrium was shifted to a somewhat higher value in this calculation because this source of particles generally elevates the particle concentration markedly with consequent increase in the daughter equilibrium. Table V shows the alpha dose for a 0.12 pm particle, the same as the nominal indoor aerosol particle, but for a particle which is assumed to be hygroscopic and grows by a factor of 4, to 0.5 pm, once in the bronchial tree.

The results in Tables II to V indicate that a range of alpha dose factors for radon daughters of about a factor of ten exists and that they are site specific depending primarily on the indoor aerosol. The potential for delivering an alpha dose four times greater or smaller than that in a nominal atmosphere exists if there is either a small sized or hygroscopic aerosol. The calculations have been performed here for males, but it has been shown that this model is easily adapted to calculating the alpha dose to women, children and infants (Harley, 1984). 

TABLE II. Alpha Dose in mGy/WLM for Occupational Mining Atmosphere. Breathing Pattern and Specific Conditions, See Footnote... 

Particle diameter 0.17 pm (AMD) for Attached Daughters Nasal Deposition 1.3% for Attached and 60% for Unattached Daughters Alpha dose to cells at 22 pm depth below epithelial surface Twenty percent alveolar deposition prior to expiration... 

Alpha dose to cells at 22 m depth below epithelial surface... 

Current lung dosimetry models are based on the assumption that basal cells of the bronchial epithelium are the critical target cells for malignant transformation and that the alpha dose to these cells is the relevant radiation dose. 

Martell, E. A., and K. S. Sweder, Properties of radon progeny in mainstream cigarette smoke and the alpha dose at segmental bifurcations of smoke, in Current Topics in Lung Dosimetry, (D. R. Fisher, ed.) pp. 144-151, CONF-820492, NTIS, U. S. Department of Commerce, Springfield, Virginia (1983). 

Investigations with Animals. A further support of the hypothesis described above can be found in investigations carried out with animals Leonard et al. (1979) found in an area with high natural radioactivity in France a small but significant increase of chromosome aberrations in the lymphocytes of rabbits. The rabbits were kept in a hut for 12 months, and received up to 0.7 Gy/year from gamma rays together with more than 6 Gy alpha doses from radon and daugthers. Further experiments with rabbits at radon exposure under controlled conditions have shown that the chromosome... 

Fisenne, I.M., Perry, P.M., Chu, N.Y., Harley, N.H. (1983). Measured 234,238U and fallout 239,240Pu in human hone ash from Nepal and Australia skeletal alpha dose. Health Phys. 44 (Suppl. 1) 457-67. 

Barretto, P.M.C., Clark, R.B. and Adams, J.A.S., 1972. Physical characteristics of radon-222 emanation from rocks, soils and minerals its relation to temperature and alpha dose. In J.A.S. Adams, W.M. Lowder and T.F. Gesell (eds.). The Natural Radiation Environment II. National Technical Information Service, US Dept, of Commerce, Springfield, Va., pp. 731-740. 

Alpha dose in LWR uranium waste from 1 MT heavy metal incorporated in 70 liters... 

Furthermore, one may think of radiation influencing the chemical stability of the solid. There is no experimental evidence for any of these effects [H2]. In all test procedures a long-term dose has been simulated in a short time, which will probably rather enhance the effects. The apparent radiation stability should be not too surprising, bearing in mind that an alpha dose of 10 /cm over 100 years is a rather modest one compared to the fast-neutron doses to which materials in a nuclear reactor are exposed. 

Lundgren D, Gillett N, Hahn F, et al. 1987. Effects of protraction of the alpha dose to the lungs of mice by repeated inhalation exposure to aerosols of plutonium-239 oxide. Radiat Res 111 201- 224. 

Mahlum D, Sikov M, Hungate F. 1976. Influence of temporal distribution of alpha dose in bone tumor induction. In Webster S, ed. The health effects of plutonium and radium. Salt Lake City, UT J.W Press, 49-56. 

Harley N, Pasternack B. 1982. Environmental radon daughter alpha dose factors in a five-lobed human lung. Health Phys 42 789-799. 

Pleochroic haloes have been used to date minerals and rocks. The method depends on the fact that the intensity of their colors increases with the alpha dose to which they have been exposed. The relationship between the two may fall into any one of three categories. In the first place, a normal stage exists in which color increases linearly with radiation dose. Secondly, there is a saturated stage in which the color reaches a maximum density and does not show any further increase with increasing radiation dose. Thirdly, there is an inversion stage in which coloration actually decreases with the intensity of the radiation dose - this is caused by extreme radiation damage. Only those from the first category are used for age determinations. 

A number of assumptions have to be made. One is that the coloration really is a linear function of the received alpha dose. A second is that concentrations of radionuclides emitting alpha particles have not altered except through radioactive decay processes. Consequently, to date a mineral using this method entails measuring the alpha activity of the inclusion at the center of the pleochroic halo as well as assessing the intensity of color of this feature. Also, it is essential to know the relationship between the alpha dose and the intensity of color in the mineral to be dated. This latter can be established experimentally by irradiation of the mineral sample with alpha particles from an artificial source or by examining haloes in other samples of the same mineral with known ages. 

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